1. Field of the Invention
The present invention relates generally to moisture detection. More particularly, the invention relates to devices for sensing moisture of a material, such as a diaper.
2. State of the Art
In the past, liquid detectors have been devised for determining the presence of moisture in an article of clothing such as an infant's diaper or undergarment. For example, U.S. Pat. No. 3,818,468 discloses a portable detector which includes first and second probes. More particularly, this patent discloses a resistive type detector which is operated by attaching the probes to the article of clothing where moisture is to be detected. When sufficient moisture exists in the layers of the material being sensed, a reduced resistance path is formed between the ends of the probes attached thereto. A signal is transmitted to indicate when the ohmic resistance drops below a pre-determined value.
Further, U.S. Pat. No. 2,579,316 relates to a pressure sensitive moisture testing instrument. This patent discloses a circuit which establishes either a current flow or an electric field through a material for which moisture is to be tested. The current flow or electric field, as the case may be, is influenced by the moisture content present in the material, causing a corresponding change in current flow or voltage in the circuit. Although column 1, lines 16-20 refer to several varieties of this general circuit, one of which includes "the dielectric type" dependent upon change in dielectric constant with variations in moisture, specific circuitry related to this type of device is not disclosed.
U.S. Pat. No. 3,824,460 relates to a capacitive sensing system for detecting the presence of a liquid on a floor or the like using a sensing probe. Two parallel wires are encased in a plastic material spaced by webbed portions made of the same material so as to form a flat cable assembly which may be installed on a floor where leakage is to be detected. Leakage on the floor causes liquid to fill into the spaces between the two wires where the web is not present, thus changing the dielectric constant between the two wires and influencing the overall capacitance of the sensor. This change in dielectric constant results in a change of current through the capacitor and is used to provide an output alarm.
Although devices for detecting moisture are known, a relatively accurate, cost effective moisture detecting device for sensing the moisture content of a material such as a diaper would be desirable.